This invention relates to spent fuel storage racks, and more particularly to a spent fuel storage rack capable of storing at high density a plurality of fuel assemblies which have been used in nuclear reactors.
In nuclear power plants, the spent fuel withdrawn from the reactor cores is temporarily stored in storage racks immersed in a pool of water or other radiation shielding liquid before being reprocessed. In recent years, there has been an increase in the amount of spent fuel removed from the reactor cores, but existing facilities have no sufficient capacity to reprocess the spent fuel at once. In order to cope with this situation, proposals have been made to use high density spent fuel storage racks. For example, Japanese Patent Kokai (Laid-Open) No. 114600/76 filed by Frank Bevilacqua discloses a storage rack of the type described. This storage rack comprises a plurality of neutron absorbing containers arranged to receive a plurality of fuel assemblies disposed vertically in an array with predetermined spaces between the adjacent fuel assemblies, each container being designed to perimentrically encircle a fuel element. The neutron absorptive containers are each rectangular in cross section. In order to form these containers into a unitary structure while maintaining the containers in predetermined spaced relationship, spacers or U-shaped channels are welded to upper end portions and lower end portions of the containers in such a manner that the spacers extend in a grid pattern between the rows of the containers and the columns of the containers. Some disadvantages are associated with this type of spent fuel storage rack. First, it is complex in construction and has many portions where the containers are joined by welding to the spacers. A difficulty is encountered in carrying out welding, and assembling of this type of rack is a time-consuming operation and requires a lot of labor. The containers are preferably hexagonal in cross section for storing fuel assemblies which are also hexagonal in cross section, in order that high density storage can be achieved in a spent fuel storage rack. However, it is practically impossible to use spacers for containers of a hexagonal cross section in the same manner as spacers are used for the containers of the rack of the type referred to above, because the spacers used will increase in number and yet the containers will be located relatively sparsely.